| The advent of a new class of optical fiber waveguides in the form of the photonic crystal fiber (PCF) in the late 1990s has enriched and extended the knowledge of fiber waveguide. The PCFs have showed many advantages in fiber delivery, amplification and many more similar applications compared with conventional fibers. The generation of ultra-broadband high brightness supercontinuum based on the special waveguide characteristics is one of the exciting applications. Because of the significance in fields such as medicine, biology, chemistry, telecommunication, precision measurement, military and so on, the supercontinuum light source based on PCFs has attracted widespread interests throughout the scientific community. Although the supercontinuum light source based on PCFs has received prosperity, there has left many unresolved theoretical and experimental problems. On one hand, because of the special waveguide characteristics, the process of pulse propagation and supercontinuum generation seems to be more complicated. The theory model and numerical simulation method need to be improved. Physical mechanisms under supercontinuum generation also need to be clarified. On the other hand, the output power of the present supercontinuum light source is so low-level. Attention should be paid on the conversion efficiency. Besides, there remains many other problems need to be researched, but those are beyond this thesis. Here, we concentrate our attention on the above two mentioned problems. Theoretical and experimental research has been careful took in aim to clarify the characteristic of pulse propagation and supercontinuum generation. A systematic technical scheme is proposed to enhance the output power and conversion efficiency. The content of this thesis is summarized as follows.The format of General Nonlinear Schrodinger Equation (GNLSE) which describes pulse propagation and supercontinuum generation in PCFs has been improved. This improvement makes it more facilitative to the reflection of the various propagation effects and the numerical simulation. The numerical method has also been improved. Several significant techniques related to the numerical simulations have been analyzed too. We treat the nonlinear term straightly as an integral instead of some mathematic approximation during the numerical calculation by the Split-Step Fourier Method (SSFM). Resolving of the integral is achieved by the Counter-Fourier -Transform of the product of the two Fourier-Transforms. The artful calculation of the nonlinear term avoided man-made approximation insures the precision. Numerical precision associated with step size choice is studied. Criteria are proposed as follows. The temporal and spatial step size can be appropriate chosen from the spectrogram. And the temporal figure provides a criterion for the temporal step size. These conclusions present some intuitionistic reference criteria for the intractable step size choice in solving the GNLSE. We have also analyzed the numerical precision of the Difference Method and the Runge-Kutta Method when calculating the nonlinear term. Results shows the Runge-Kutta Method can achieve much higher precision. All of these conclusions provided useful guidance in describing and numerical calculating the pulse propagation and supercontinuum generation in PCFs.Detail analysis of dispersion and nonlinear effect in the process of pulse propagation and supercontinuum generation in PCFs is carried out by the improved model and numerical method. PCFs parameters and pump parameters which may influence the supercontinuum light source are treated as variables to analyze their impact on the supercontinuum output. Theoretical and experimental research has clarified the mechanisms and affections under different cases. Optimized supercontinuum light source projects are proposed separately in the normal and anomalous dispersion region.The conversion efficiency of supercontinuum light source is divided into the whole system conversion efficiency and the efficiency conversion at certain band. Theory study shows results as follows. The efficiency conversion at certain band can be enhanced by optimizing the PCFs and the pump source. The whole system conversion is related to either the coupling efficiency or the extent of pump laser translated into the supercontinuum. The former can be enhanced by designing a high efficiency couple system. And the later can be achieved by optimizing the PCFs length.On the basis of these theory studies, supercontinuum generation experiments are carried out by pumping different PCFs by a conventional solid-state laser and a fiber laser. Preferable anticipated experimental results are obtained. So the veracity and validity of our model and numerical method is proved. And the physical mechanisms as well as the key experimental techniques are clarified. Emphasis is put on enhancing the whole system conversion efficiency. High efficiency coupling methods under different pumping conditions are also explored. These studies provide useful experimental guidance for developing the high power and high efficiency supercontinuum light source.A whole system project of high power and high efficiency supercontinuum light source is proposed based on the systematic theoretical and experimental studies. Optimized designs of pumping source, PCFs, coupling system and other related are proposed too in order to overcome the limitation of the output power and conversion efficiency. |
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